![]() ![]() These innovations include sequencing-by-synthesis, sequencing-by-ligation, ion semiconductor sequencing, and others. The term “NGS” does not denote a single technique rather, it refers to a diverse collection of post-Sanger sequencing technologies developed in the last decade. Here we discuss how NGS is exquisitely capable of revealing both types of variants in patients’ genomes. Such genomic differences-called “variants”-fall into two classes: (1) changes to the DNA sequence, e.g., the single-nucleotide polymorphisms (“SNPs”) and short insertions/deletions (“indels”) in the CFTR gene that can cause cystic fibrosis, and (2) large deletions/duplications (“del/dups”, a.k.a., “copy-number variations” or “CNVs”), e.g., the whole-gene deletions of HBA1 and HBA2 that largely determine the presence and severity of alpha-thalassemia. The clinical utility of an NGS-based test stems from its ability to confidently identify the differences between a patient’s genome and the reference genome. These advances have allowed NGS-based tests to enter the clinic, where they are an exponentially growing presence in carrier screening, testing for fetal aneuploidies, detecting the presence of rare diseases, and assessing both the risk and existence of cancer. ![]() Remarkably, not even 15 years after decoding the first human genome, NGS techniques now enable the sequencing of an entire human genome in a single day for around $1000. Therefore, in order for the theoretical promise of personalized genomic medicine to become a clinical reality, a quantum leap in sequencing technology was required. Unfortunately, by the end of the Human Genome Project in 2002, this mature sequencing technique was already operating at nearly peak efficiency, making it totally unsuitable for scaling up to the task of sequencing millions of patients’ genomes quickly and affordably. The effort involved hundreds of researchers around the world and was a tour de force of the “first-generation” Sanger sequencing technology developed in the 1970s. where the agencies (or power companies) have installed gauges to monitor water flows and levels.Assembly of the first human genome sequence consumed 12 years and cost nearly $3 billion. ![]() Examples of this situation are the large reservoirs in the Rockies and Western U.S. Some river or dam/pool water level gauges will be referred to using feet (or meters) above mean sea level (MSL). This bottom limit/reading of these gauges is usually due to the position of the gauge in or along the river. In contrast, a few river gauges will not read below a certain level (which may be above it's respective gauge zero). When they do go below zero, it is usually a sign of a prolonged dry spell. Not many sites in the region actually go below zero ( Renovo and Williamsport are two examples that do). There is a collaboration between many government agencies in order to settle on a gauge zero, and which Datum (way of mapping the earth) will be used as a basis. If the level was to change up or down just to avoid having a negative value, it might become confusing for them to remember the new level which would impact their home. ![]() They know that the water reaches the front steps of their house at 17 feet (using the current values). If the gauge zero level was changed on a whim, all the historical data for the gauge site could be rendered useless or at least very confusing.įor example, it may be difficult to explain to people who have been used to having a certain river level/guage reading as a personal threshold. Still, the gauge zero datum levels are not changed to keep continuity.įor example, most of the gauges in the Susquehanna Basin experienced their record Flooding during Agnes in 1972. Silt may deposit in the river channel over time (filling the channel up), or the channel bottom may be scoured out to a deeper level by strong currents. These gauge zero levels are not changed very often. That gauge zero level is chosen considering many factors, like the USGS references (or benchmarks) that are near to the gauge site, or an historical level that may have been used for a hundred years or more. It means that the gauge is reading at or below the agreed-upon zero level. In summary, when a river gauge reads zero or in the negative numbers - it does not mean that the river has gone totally dry or is running below ground. A river's stage at a point (a gauge reading) is not an absolute measure of the depth of the water in the channel, rather it is a depth with respect to an historical Datum level. ![]()
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